Unitary combination of pressure-responsive flow control unidirectional valves for hydraulic systems



United States Patent [72] lnventor Johannes Vagn Baatrup Sonderborg, Denmark [21] Appl. No. 768,110 [22] Filed Oct. 16, 1968 [45] Patented Dec. 29, 1970 [73] Assignee Danfoss A/S Nordborg, Denmark a company of Denmark [32] Priority Oct. 17, 1967 [3 3 1 Germany [54] UNITARY COMBINATION OF PRESSURE- RESPONSIVE FLOW CONTROL UNIDIRECTIONAL VALVES FOR HYDRAULIC SYSTEMS 7 Claims, 2 Drawing Figs.

[52] U.S.Cl 137/111, 1 37/5 96. 12 [51] Int. Cl ..G05d 11/00 [50] Field ofSearch 137/111,

596.12/lnquired, 596.13

[56] References Cited UNITED STATES PATENTS 2,607,599 8/1952 Kanuch l37/596.l2 FOREIGN PATENTS 251,474 5/1964 Australia 137/111 69.912 10/1958 France Primary Examiner-William F. ODea Assistant Examiner-David J. Zobkiw Art0rneys-- Robert E. Burns and Emmanuel J. Lobato l37/lll valve-closing positions by separate springs, controlling the pressures at which the internal pistons reciprocate relative to the transporting outer hollow pistons, from the spring pressure applied to the hollow pistons biasing the hollow transporting pistons away from each other thus causing the unidirectional valves formed to respond to different pressures in opening and closing. Spheres cooperating with the internal pistons form another pair of check valves which are pressure-responsive and can also be opened by a rigid control member, in the form of a rod, when the hollow pistonsare driven in axial directions toward each other by given fluid pressures. The fluid under pressure is applied to the valves by entry into and out of two axially spaced spaces defined in the bore by the hollow transporting pistons and an intermediate space therebetween.

Pmmgnumzsmm 3550.611

INVENTOR. JOHANNES VAGN BAATRUP UNITARY COMBINATION OF PRESSURE-RESPONSIVE FLOW CONTROL UNIDIRECTIONAL VALVES FOR HYDRAULIC SYSTEMS to flow into a return line from a motor and junction lines between control devices and the motor to maintain pressures that do not exceed a safe value, while other check valves enable fluid under pressure to be taken from the return line when the pressure is too low. Excesspressure and low pressure can occur in a hydraulic system, for example, due to heating up or cooling of the fluid under pressure. The moving parts of the fluid motor in the system are also freqq'ently subjected, during operation, to a hydraulic shockdue to an external impact, for example when a hydraulic piston is used in a fluid motor for guiding the wheels of a vehicle which strike an obstacle. Considerable excess fluid pressure then occurs on one side of the piston and too low a pressure on the iother, and this can be balanced out through the check valves Control devices in known hydraulic; system usually incorporate a control member of some kind, e. g. a rotary slide, which, in a neutral position, provides a bypass to a motor in the system. The control element is then under the influence of the pressure in a bypass on the one side, and on the other side it is under the influence of the pressure in lines connected to the motor. Even at quite small differences in pressure, the control member in such control devices can jam, or at least be prevented from operating properly.

Such fluid pressure difierences can arise, for example, if a second device, 'e.g. a control device for a second motor, is connected to the control device for the first motor. Thus, if

the first control device is in its neutral operating position and sure in the system operates unilaterally on the control member of this control device. a

It is a principal object of the present invention to provide a unitary valve arrangement to remove the difficulties occurring as a result of pressure differences in hydraulic systems.

The invention provides a valve combination of the initially described kind and provides, in both supply lines to a motor valves that are opened when a pressure obtains in both motor lines that exceeds the pressure in a return pipe by a prescribed amount. In a valve arrangement according to the invention two valves of two pairs of check valves 'open towards the motor and are able to equalize the pressure when a smaller or greater excess pressure obtains in a bypass of a control device in the hydraulic circuit. The valves opening away from the motor on the other hand cannot be used to equalize excess pressure in the motor supply lines that, while giving trouble, has not yet reached the limit of safety, since these latter valves are biased under spring pressure such that they only open when a quite high safety value for fluid pressure has been exceeded. In such a case, however, the above-mentioned valves of the invention can be used since these open in a circumstance where a limiting value for pressure that can be considerably lower than the safe pressure is exceeded in both motorsupply lines.

It is particularly advantageous to provide valves of both pairs of check valves of the invention, with additional means which are influenced by the pressure in both motor supply lines and which enable the valves to open in a positive manner, i.e. independently of their usual mode of actuation. In this way, no additional check valve is required in the lines of the system. In particular, the additional means can act upon those valves of the two pairs that open toward the motor. These valves can take over the additional function that much sooner, since the spring associated with them is not so strong as is the case with the two other valves in the two pairs of check valves.

The unitary valve combination of the invention comprises two pistons displacable in response to fluid pressure symmetrically relative to a central common stop in a common bore which is closed at its opposite ends and near the end-faces of which spaces are formed for connection to motor supply lines and in the middle of which an intermediate space is in connection with a returnpipe. The pistons each are hollow and have at their end-faces or crowns ,an inner seat for other hollow check valve elements comprising other pistons contained in the pistons. These other pistons in turn have on their end-faces a first-mentioned hollow seat for a third pair of check valve elements. The two first-mentioned pair of check valve elements are biased by a common spring supported on the two pistons and extending between them. A rigid rod extending through the two pairs of pistons and is of such length that when both pairs of hollow pistons are displaced toward each other up to the central stop, the third pair of elements of the second check valves are lifted from their seats, but when only one set of pistons is displaced up to the stop, the second check valves are unaffected. In this way, four valves having six pressure control functions are assembled in an extremely compact space and without need of three sets of separate unidirectional or check valves.

In the construction described, the pistons have valve openings in the crowns and comprise, outside of the inner pistons, adjacent their valve seats, extending in the axial direction, a guide passage, containing openings, for the second check valve elements, which, constitute simple spheres or balls. The second check valve members, the first check valve I members and their springs and backing rings later described can be inserted into the bore from an open end, later closed, and the whole assembly locked in position by means of a circlip.

The arrangements rigid control rod has near both ends thereof a stop-face which bears against an opposed face on the first check valve hollow pistons. This rod causes positive opening of both of the second pair of check valves even when the pressures in the two motor supply and discharge lines are not exactly the same.

The invention will now be described in more detail by reference to an embodiment illustrated in the drawing, wherein:

FIG. 1, is a schematic diagram of a valve arrangement of the invention connected in a hydraulic system; and

FIG. 2, is a longitudinal section view of a unitary valve combination according to the invention.

FIG. 1 illustrates a pump 1 delivering hydraulic fluid under pressure pressure from a supply source 1 by way of a discharge line 3 to a first control device 4 in a return line 5 in which is connected a second control device 6 from which the hydraulic fluid can return to the source 2 through a line 7. The first control device 4 has a neutral position, in which the fluid is fed directly from the discharge line 3 into the return line 5 through a bypass 8, and has two working positions, in which the hydraulic fluid can be selectively delivered through two hydraulic motor junction lines 9, 10 into two chambers 11, 12 formed on both sides of a piston 13 of a hydraulic cylinder 14. The junction lines 9, 10 are each both supply and discharge lines to and from the motor 14 and are referred to as junction lines for convenience. The second control device 6 likewise has a bypass and at least one working position, not shown, in which this bypass is blocked.

The first control device 4 can control, for example, the motor 14 for guiding the wheels of an agricultural machine, and the device 6 may have a motor on the machine, not

1 shown, for lifting a load. Two connecting lines l5, 16 lead tains a pair of check valves, namely first check valves 18, 19, which open away from the motor, are subjected to the force of a strong closing spring, and, in principle, should only open when the pressure in the associated junction line exceeds a safe pressure, and two check valves 20, 21 which open toward the motor, opened by a relatively small pressure force, and, when the pressure is too low, allow hydraulic fluid to pass from the return line into the junction lines.

Each connecting line 15, 16 also contains a check valve 22, 23 which is controlled by an additional actuating or control device 24 which, as indicated in dash-and-dot lines, is influenced by the pressure in the two junction lines 9, 10 and in the return line 5. The last pair of valves open when the pressure in the two junction lines 9, 10 reaches a prescribed value in excess of the pressure in the return line 5.

In its practical form, the hydraulic system will, of course, incorporate numerous safety valves and accessories, which are not shown in the drawing for the sake of clarity. ln principle, when the system is operating, the three following conditions are of importance:

l. A force K, acting on the piston 13, is too great, as result, for example, of the guided wheels on the vehicle, not shown, striking an obstacle. Excess pressure then occurs in the hydraulic cylinder chamber 11 and a pressure that is too low occurs in the hydraulic cylinder chamber 12. Hydraulic fluid under pressure passes from the one chamber 11 into the other chamber 12 through the connecting line 15, the check valve 18, which opens in this case, the check valve 21 and the connecting line 16.

ll. The first control device 4 is in a neutral position, and the control device 6 in a working position. A high pressure obtains in the return line 5. This pressure may be substantially in excess of the pressure in the motor junction lines 9, 10. The control member, e.g. the rotary slide, in the first control device 4 is loaded from the discharge line 3 and return line 5. This excess pressure is rapidly equalized by way of the two check valves 20, 21 opening toward the hydraulic motor 14.

III. A high pressure obtains in the entire hydraulic system. The first control device 4 is in its neutral position, and the second control device 6 is placed in its neutral position. The pressure in the return line then falls considerably below the pressure in the junction lines 9, 10. The control member in the first device 4 is loaded from the junction lines. ln this case, the check valves 18, 19 are unaffected, since they are too heavily biased and the other check valves 20, 21 are not influenced because their opening direction is not the right one. The third set of check valves 22, 23 however, do open, because their actuating or control device 24 determines that the pressure in the two junction lines 9, has exceeded that in the return line 5 by a predetermined amount.

In the unitary valve construction shown in FIG. 2, the check valves and control device 18-24 with the corresponding connections are grouped together with connections to the fluid lines -17. A single bore 25 in a housing is sealed at both ends by means of caps or plugs 26.

The connecting lines 15, 16 are connected to ports near the ends of the bore and the return line 17 in the middle of the bore. Two pistons 27, 28 are disposed in the bore and can move in the bore axially, from a stationary position illustrated, up to a central stop 29. Each piston is hollow and has on the inside of its end-face or crown a valve seat 20, 30, 31, about a valve opening, for a valve member or element 32, 33 of the first pair of check valves which are acted upon by relatively strong springs 34. 35 which bear against backing rings 38, 39 secured by circlips 36, 37. These valve elements or members 32, 33 are hollow pistons reciprocable relative to their transporting pistons 27, 28 and their outwardly directed end-faces 40, 41 constitute valve seats for a third pair of check valve members 42, 43 of the second pair of check valves. These latter members or elements are formed as balls or spheres. Beyond their valve seats, the pistons comprise guide passages 46, 47 for these spheres. The passages are provided with openings 44, 45. Thus spaces of varying volume are formed at extremities of the bore in communication with the connecting lines 15, 16 through respective portsfor inward and outward flow of fluid. A space intermediate these extremity spaces is formed between the transporting pistons 27, 28 and it is in communication with the return line 17 for inward and outward flow of fluid.

A spring 48 extends between the first pair of valve pistons 32, 33. Also, on the bore longitudinal axis is disposed a control rod 49 having ends 50, 51 coaxial with valve openings in the pistons 27. 28, 32 and 33 and are able to lift the ball valve elements or members 42, 43 from their seats. The rod is provided with axial groves 52, 53 and can bear on terminal or ends of the inner bores of the valve members or inner pistons 32, 33 by means of stop-faces 54, 55.

Referring again to the three operating conditions described above, the functions are as follow:

I. When excess pressure occurs in the line 15, the piston 27 moves toward the right up to the stop 29, and its internal valve member 32 is transported to the right and the pressure overcomes the force of the two biasing springs 34, 48 and the inner valve unseats so that fluid flows from the line 15 into the central cavity or space 56. From there the fluid can flow away by way of the return line 17 or, if too low a pressure obtains in a 25 junction line 16, causing the right valve ball member 43 to lift from its seat, the hydraulic fluid can pass thereby by way of the piston extension openings 45.

11. When the pressure in the return line 17 is in excess of that in the connecting lines 15, 16, the two ball check valve members 42, 43 are lifted, so that the excess pressure can be equalized.

111'. When the pressure in the connecting lines 15, 16 is in excess of that in the return line 17, the two pistons 27, 28 are moved inwards until they bear against the stop 29. This shortens the distance between the two ball valve members 42, 43 so that they are lifted from their seats by the control rod 49 and the excess pressure is balanced out.

Comparison of the functions detailed in the paragraphs l' to 111 above shows that the length of the rigid control rod 49 in relation to the distances over which the hollow pistons 27, 28 move must be such that the rod does not lift the ball check valve members 42, 43 when one hollow piston is displaced, but positively lifts them'when both pistons are displaced.

While the unitary valve combination combination according to the invention has been described as applicable to the above-described hydraulic system it is to be understood that it may be used in other hydraulic systems in which this combination may perform similar functions.

While a preferred embodiment of the invention has been shown and described it will be understood that many modifications and changes can be made within the true spirit and scope of the invention.

lclaim:

1. A unitary valve combination comprising, means defining a housing having a bore closed at opposite ends, a first pair of individually reciprocable valve elements in said bore reciprocable in said bore in response to fluid under pressure defining a central space of varying volume in said bore and two axially spaced extremity spaces of varying volume defined by said first pair of valve elements adjacent opposite ends of said bore and separate from said central space, said housing having two ports each in communication with said extremity spaces for fluid flow under pressure alternatively into and out of said extremity spaces and a port in communication with said central space forfluid flow alternatively into and out of said central space, a second pair of valve elements each transported by an associated one of said first pair of valve elements and reciprocable relative to the transporting first pair of valve elements and jointly defining therewith unidirectional check valves allowing fluid from said extremity spaces to said central space, means determining the fluid pressure at which said first and second pairs of valve elements are relatively reciprocable determining the pressure at which said check valves will open, a third pair of valve elements each cooperative with a respective one of said second pair of valve elements defining other without rendering the second pair of valve elements reciprocable relative to the first pair of elements rendering said other unidirectional check valves effective to allow fluid flow from said central space to said extremity spaces.

2. A unitary valve combination according to claim 1, in which said first pair of 'valve elements comprise hollow pistons.

3. A unitary valve combination according to claim 2, in which said hollow pistons each comprise a crown having an opening and a valve seat circumferentially of said opening internally of the piston, and said second pair of valve elements comprising internal pistons internally of said hollow pistons seated on said seat and unseatable therefrom in response to fluid pressure defining the first-mentioned check valves.

4. A unitary valve combination according to claim 3, in which said internal pistons each comprise an opening coaxial with the hollow piston openings providing communication between the extremity spaces and said central space and each comprise a seat circumferential of the internal piston opening, said third pair of valve elements each comprising a sphere seatable on a respective seat of an internal piston defining said second set of check valves.

5. A unitary valve combination according to claim 4, in which all of said pistons are coaxial and in which said control member comprises a rigid rod coaxial with said piston openings unseating both of the spheres only when both of said hollow pistons move axially toward each other a selected extent in response to fluid pressures in said spaces, and means biasing the hollow pistons apart.

6. A unitary valve combination according to claim 5, inc luding stop means for limiting the axial travel of said hollow pistons in said bore in a direction toward each other thereby to limit the least volume dimension of said central space and other stop means to limit the extent of travel of said hollow pistons toward said opposite ends of said bore thereby to insure the hollow pistons do not travel to said opposite ends and a least volume dimension of said extremity spaces is defined.

7. A unitary valve combination according to claim 6, including axially spaced stop faces on said rod for stopping axial travel of said internal pistons relative to said rod in directions away from said opposite ends. 

